A number of costly and/or hazardous situations can arise from positional uncertainties along a well bore trajectory and from uncertainties of the locations along that trajectory relative to logs of formation properties taken in the same well. In particular, the following are examples of problems that may result from positional errors:
In highly developed fields, positional errors may result in well bore collisions. The intersecting of different well bores may result in undesirable interactions between the activities in different well bores, including damage to tubing strings, and unexpected fluid exchange.
When geosteered drilling is employed in fields with a known geological model, positional errors may result in drilling decision errors. Measured formation properties may be associated with incorrect beds in the model, causing the drillers to steer the well bore trajectory along a misidentified bed or into a misidentified area.
Positional errors can further make operators unable to determine the cause of discrepancies between a geologic model and logs. When such discrepancies are attributable to positional errors, the operator cannot determine whether the model itself is incorrect. (As a byproduct, the difference in resolution between available position measurement techniques and the vertical resolution of most logging while drilling (“LWD”) sensors makes it difficult to correlate logs with formation evaluation data used to create the geologic models.)
Most fundamentally, positional errors can prevent a driller from achieving optimal placement of well completions, and may even result in wandering from lease lines. Each of the foregoing issues may reduce the efficiency with which petroleum can be produced from a reservoir.